Brewing a true lager takes a little bit more work and specialized equipment than brewing an ale. The most important factors in brewing a good lager outside of recipe formulation are: yeast strain selection, pitch rate, and fermentation temperature.
YEAST STRAIN SELECTION:
Once the recipe has been chosen, the next task that will have the biggest impact on the final beer is yeast strain choice. Home brewers have a wide selection of lager strains to choose from. The strain should be chosen based on the style of beer, the fermentation temperature, original gravity, and time available for conditioning or lagering.
Lagers typically have a reduced ester profile and are characterized as clean with discernible malt character. It is very important to recognize that pitch rate is directly related to ester production. Increasing the quantity of yeast pitched is the most effective method of reducing the ester profile in the finished beer. A minimum of 12 million cells/mL is recommended to keep esters at a minimum.
One Wyeast ActivatorTM pack will deliver about 6 million cells/mL to 5 gallons (19 L) of wort. In order to increase this rate to 12 million cells/mL it is necessary to either pitch two ActivatorsTM or to make a 0.5 gallon (2 liter) starter with an ActivatorTM.
One of the most common questions we field is, “should I start my lager warm or cold?” The answer depends on how much time you have for your primary fermentation and how clean you want your final beer. The best results will be achieved by pitching at least 12 million cells/mL into cold and well-aerated wort at 48-58 °F (9-15 °C).
If a faster primary fermentation is desired or you are pitching less yeast, then it is best to start a little bit warmer and then cool to the desired fermentation temperature once signs of fermentation are evident.
A secondary fermentation at a temperature below the primary fermentation allows for a slow reduction of any remaining fermentable sugars. This secondary fermentation can take from one to three weeks at temperatures starting between 39-41 °F (4-5 °C) and slowly falling to as low as 33 °F (1 °C). The length of the secondary depends on the amount of fermentable sugars remaining.
During fermentation the yeast produces several different compounds, one considered an off flavor is Diacetyl, which gives a buttery flavor to the beer. During primary fermentation the yeast has the capacity to remove diacetyl. Since it is temperature dependent a raise will increase production, or the yeast will breakdown diacetyl into acetoin and 2,3-Butanediol at the middle of the primary fermentation.
Diacetyl reduction also takes place during secondary fermentation. Depending on the beer profile standard, once the fermentation process reaches 40 to 50% attenuation the temperature is raised 3 to 5 degrees to allow the yeast to reabsorb the diacetyl and break it down to Acetoin, then into 2,3 butanediol. After determining there is no more diacetyl present, the beer cooling process starts.
Example Diacetyl Rest Schedule:
Assuming the gravity is 1.048, once the wort drops to around 50% attenuation, the temperature is raised 2 degrees Fahrenheit or according to your beer specifications as in the following schedule:
|1||54 °F (12 °C)||1.048|
|2||54 °F (12 °C)||1.046|
|3||54 °F (12 °C)||1.033|
|4||54 °F (12 °C)||1.021|
|5||56 °F (13 °C)||1.010||Raise temperature 2 degrees Fahrenheit or according to your beer specifications|
|6||56 °F (13 °C)||1.0098|
|7||56 °F (13 °C)||1.009|
|8||56 °F (13 °C)||1.009|
The diacetyl rest may take 6 days after raising the temperature at 56 °F (13 °C). The beer should be evaluated at this point to determine that it is not perceived or sensed.
Going above this temperature range will depend on the fermentation set temperature. If primary fermentation is set at 56 °F (13 °C), there is no other choice to raise the temperature to 57 °F (14 °C). Likewise, depending on your beer specifications in some cases it is possible to raise the temperature a bit higher.
Diacetyl may also be present if there is a Lactobacillus and Pediococcus contamination.
CONDITIONING OR LAGERING:
Lagering is a time when harsh flavors from fermentation are mellowed. Yeast re-absorb some of the ester compounds from fermentation as well as some of the sulfur compounds. Malt tannins coagulate with haze-forming proteins and precipitate out along with some sulfurous compounds.
Temperatures should remain very stable during lagering, generally in the range of 33-34 °F (1-2 °C). Contact with oxygen at this point is very detrimental to beer flavor and should be avoided at all costs. Lagering time depends on many factors. If a cold secondary fermentation was employed, then the length of the lagering period can generally be decreased. A lagering period of one to four weeks is typical.